1. Field of the Invention
The present invention relates to an organic electroluminescence device (hereinafter also referred to as “organic EL device”). In particular, the invention relates to an organic electroluminescence device with excellent light emitting characteristics.
2. Description of the Related Art
In recent years, organic electroluminescence devices are being actively researched and developed because light emission with high brightness is obtained by low-voltage driving. In general, organic EL devices are configured of organic layers including a light emitting layer and a pair of electrodes interposing the foregoing layers therebetween and are one in which an electron injected from a cathode and a hole injected from an anode recombine with each other in the light emitting layer, and energy of a formed exciton is utilized.
In recent years, high efficiency of the device is being advanced by using a phosphorescent material. Iridium complexes, platinum complexes and so on are known as the phosphorescent light emitting material (see, for example, U.S. Pat. No. 6,303,238 and WO 00/57676). However, devices capable of satisfying both high efficiency and high durability have not been developed yet, and it is the present situation that it is eagerly desired to develop a phosphorescent material capable of satisfying the both.
There is disclosed an organic electroluminescence device containing, in a light emitting layer, a material of a tetradentate-coordinated platinum complex which is composed of a tetradentate ligand having one azine ring, one azole ring and two aromatic hydrocarbon rings and in which a nitrogen atom of the azine ring and a nitrogen atom of the azole ring form a coordinate bond together with a platinum atom (see, for example, JP-A-2006-261623 and JP-A-2008-37848). However, it may not be said that such an organic electroluminescence device is sufficient from the standpoints of luminous quantum efficiency, driving voltage and durability, and further improvements have been desired.